Method of forming a layer on a substrate to facilitate fabrication of metrology standards

ABSTRACT

The present invention is directed to a method of forming a layer on a solidified portion of a substrate that facilitates fabrication of metrology standards. The method features defining a planarity of the layer, which is formed by creating a flowable region on the solidified portion of the substrate, as a function of the volume of the flowable material in the region. Recognizing that the topology of a substrate upon which the layer is formed is not planar, on the nano-scale, the present invention is directed to fabricating high resolution features on the substrate and transferring the features into a solidified region of the substrate. Specifically, by minimization of the layer thickness while maximizing the planarity of the interface of the layer with the solidified portion of the substrate, it was found that very small features may be precisely and repeatably formed in the substrate.

[0001] The field of invention relates generally to imprint lithography.More particularly, the present invention is directed to forming layerson a substrate to facilitate fabrication of high resolution patterningfeatures suited for use as metrology standards.

[0002] Metrology standards are employed in many industries to measurethe operation of varying equipment and processes. For semiconductorprocesses, a typical metrology standard may include grating structures,L-shaped structures and other common patterning geometries found onproduction devices. In this manner, the metrology standards facilitatemeasurement of the performance of the processing equipment.

[0003] Conventional metrology standards are manufactured from a varietyof conventional processes, such as e-beam lithography, opticallithography, and using various materials. Exemplary materials includeinsulative, conductive or semiconductive materials. After formation ofthe metrology standards using conventional processes, a post processcharacterization technique is employed to measure the accuracy of themetrology features. This is due, in part, to the difficulty inrepeatably producing reliable accurate metrology standards. A drawbackwith the conventional processes for manufacturing metrology standards isthat the post process characterization step is time consuming. Inaddition, the difficulty in repeatably producing reliable metrologystandards results in a low yield rate. A processing technique that mayprove beneficial in overcoming the drawbacks of the conventionalprocesses for fabricating metrology standards is known as imprintlithography.

[0004] An exemplary imprint lithography process is disclosed in U.S.Pat. No. 6,334,960 to Willson et al. Willson et al. disclose a method offorming a relief image in a structure. The method includes providing asubstrate having a planarization layer. The planarization layer iscovered with a polymerizable fluid composition. A mold makes mechanicalcontact with the polymerizable fluid. The mold includes a reliefstructure, and the polymerizable fluid composition fills the reliefstructure. The polymerizable fluid composition is then subjected toconditions to solidify and polymerize the same, forming a solidifiedpolymeric material on the planarization layer that contains a reliefstructure complimentary to that of the mold. The mold is then separatedfrom the solid polymeric material such that a replica of the reliefstructure in the mold is formed in the solidified polymeric material.The planarization layer and the solidified polymeric material aresubjected to an environment to selectively etch the planarization layerrelative to the solidified polymeric material such that a relief imageis formed in the planarization layer. Advantages with this imprintlithography process are that it affords fabrication of structures withminimum feature dimensions that are far smaller than is providedemploying standard semiconductor process techniques.

[0005] It is desired, therefore, to provide a method for reliablyproducing precision features on a substrate for use as metrologystandards.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to a method of forming a layeron a solidified portion of a substrate that facilitates fabrication ofmetrology standards. The method features defining a planarity of thelayer, which is formed by creating a flowable region on the solidifiedportion of the substrate, as a function of the volume of the flowablematerial in the region. Recognizing that the topology of a substrateupon which the layer is formed is not planar, on the nano-scale, thepresent invention is directed to fabricating high resolution features onthe substrate and transferring the features into a solidified region ofthe substrate. Specifically, by minimization of the layer thicknesswhile maximizing the planarity of the interface of the layer with thesolidified portion of the substrate, it was found that very smallfeatures may be precisely and repeatably formed in the substrate. Tothat end, the method includes creating a flowable region on thesubstrate. The flowable region has a volume associated therewith.Thereafter, a layer is defined in the flowable region to have opposedsides and an area associated therewith. One of the opposed sides facesthe substrate, defining an interface thereat. The remaining side facesaway from the substrate, and the layer has a thickness measured betweenthe opposed sides. The volume is selected to maximize the planarity ofthe interface over the area. Specifically, for a given layer thickness,e.g., 10 nanometers, the volume of the flowable region determines thearea of the substrate to be covered by the layer that maximizes theplanarity of the interface.

[0007] In another embodiment, the flowable region is formed from a beadof polymerizable liquid to form the layer using imprint lithography. Tothat end, another method in accordance with the present inventionincludes depositing a bead of polymerizable liquid upon the substrate.The bead has a volume associated therewith and is spread over an area ofthe substrate by contacting the bead with a mold. The mold has aplurality of relief structures, defined by multiple recessions andprotrusions, formed into the mold surface. The contact with the molddefines a layer having first and second opposed sides. The first sidefaces the substrate and has a planarity associated therewith. The secondside faces away from the substrate and has a plurality of recessestherein. Each of the recesses has a nadir. The thickness of the layer ismeasured between the first side and a plane that is coplanar with eachnadir associated with the plurality of recesses. The planarity isdefined by the volume. Thereafter, the layer is subjected to conditionsto polymerize the polymerizable material, forming a polymerized layer.Thereafter, subsequent processes, such as etching may or may not occur.These and other embodiments are described more fully below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a simplified elevation view of a lithographic system inaccordance with the present invention;

[0009]FIG. 2 is a simplified representation of material from which animprinting layer, shown in FIG. 1, is comprised before being polymerizedand cross-linked;

[0010]FIG. 3 is a simplified representation of cross-linked polymermaterial into which the material shown in FIG. 2 is transformed afterbeing subjected to radiation;

[0011]FIG. 4 is a simplified elevation view of the mold spaced-apartfrom the imprinting layer, shown in FIG. 1, after patterning of theimprinting layer;

[0012]FIG. 5 is a detailed view of the imprinting layer shown in FIG. 4demonstrating the non-planarity of substrate;

[0013]FIG. 6 is a detailed view of the imprinting layer shown in FIG. 5showing the transfer of the features in the imprinting layer into thesubstrate during an etching process;

[0014]FIG. 7 is a detailed view of the substrate shown in FIG. 6 aftercompletion of the etch process that transfers features of the imprintinglayer into the substrate;

[0015]FIG. 8 is a perspective view of the substrate shown in FIGS. 1-7;

[0016]FIG. 9 is a detailed view of a mold shown in FIG. 1, in accordancewith one embodiment of the present invention;

[0017]FIG. 10 is a detailed view of the imprinting layer shown in FIG. 4using a planarization layer to overcome the non-planarity of thesubstrate, in accordance with a second embodiment of the presentinvention;

[0018]FIG. 11 is plan view of the substrate shown in FIG. 10, with apatterned imprinting layer being present; and

[0019]FIG. 12 is a plan view of the substrate shown in FIG. 11 afteretching of the pattern into planarization layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Referring to FIG. 1, a lithographic system in accordance with anembodiment of the present invention includes a substrate 10, having asubstantially planar region shown as surface 12. Disposed oppositesubstrate 10 is an imprint device, such as a mold 14, having a pluralityof features thereon, forming a plurality of spaced-apart recessions 16and protrusions 18. In the present embodiment, recessions 16 are aplurality of grooves extending along a direction parallel to protrusions18 that provide a cross-section of mold 14 with a shape of a battlement.However, recessions 16 may correspond to virtually any feature requiredto create an integrated circuit. A translation device 20 is connectedbetween mold 14 and substrate 10 to vary a distance “d” between mold 14and substrate 10. A radiation source 22 is located so that mold 14 ispositioned between radiation source 22 and substrate 10. Radiationsource 22 is configured to impinge radiation on substrate 10. To realizethis, mold 14 is fabricated from material that allows it to besubstantially transparent to the radiation produced by radiation source22.

[0021] Referring to both FIGS. 1 and 2, a flowable region, such as animprinting layer 24, is disposed formed on surface 12. Flowable regionmay be formed using any known technique such as a hot embossing processdisclosed in U.S. Pat. No. 5,772,905, which is incorporated by referencein its entirety herein, or a laser assisted direct imprinting (LADI)process of the type described by Chou et al. in Ultrafast and DirectImprint of Nanostructures in Silicon, Nature, Col. 417, pp. 835-837,June 2002. In the present embodiment, however, flowable region is formedusing imprint lithography. Specifically, flowable region consists ofimprinting layer 24 deposited as a plurality of spaced-apart discretebeads 25 of material 25 a on substrate 10, discussed more fully below.Imprinting layer 24 is formed from a material 25 a that may beselectively polymerized and cross-linked to record a desired pattern.Material 25 a is shown in FIG. 3 as being cross-linked at points 25 b,forming cross-linked polymer material 25 c.

[0022] Referring to FIGS. 1, 2 and 4, the pattern recorded by imprintinglayer 24 is produced, in part, by mechanical contact with mold 14. Tothat end, translation device 20 reduces the distance “d” to allowimprinting layer 24 to come into mechanical contact with mold 14,spreading beads 25 so as to form imprinting layer 24 with a contiguousformation of material 25 a over surface 12. In one embodiment, distance“d” is reduced to allow sub-portions 24 a of imprinting layer 24 toingress into and fill recessions 16.

[0023] To facilitate filling of recessions 16, material 25 a is providedwith the requisite properties to completely fill recessions whilecovering surface 12 with a contiguous formation of material 25 a. In thepresent embodiment, sub-portions 24 a of imprinting layer 24 insuperimposition with protrusions 18 remain after the desired, usuallyminimum distance “d”, has been reached, leaving sub-portions 24 a with athickness t₁, and sub-portions 24 b with a thickness, t₂. Thicknesses“t₁” and “t₂” may be any thickness desired, dependent upon theapplication. Typically, t₁, is selected so as to be no greater thantwice width u of sub-portions 24 a, i.e., t₁≦2u.

[0024] Referring to FIGS. 1, 2 and 3, after a desired distance “d” hasbeen reached, radiation source 22 produces actinic radiation thatpolymerizes and cross-links material 25 a, forming cross-linked polymermaterial 25 c. As a result, the composition of imprinting layer 24transforms from material 25 a to material 25 c, which is a solid.Specifically, material 25 c is solidified to provide side 24 c ofimprinting layer 24 with a shape conforming to a shape of a surface 14 aof mold 14, shown more clearly in FIG. 4.

[0025] Referring to FIGS. 1, 2 and 3 an exemplary radiation source 22may produce ultraviolet radiation. Other radiation sources may beemployed, such as thermal, electromagnetic and the like. The selectionof radiation employed to initiate the polymerization of the material inimprinting layer 24 is known to one skilled in the art and typicallydepends on the specific application which is desired. After imprintinglayer 24 is transformed to consist of material 25 c, translation device20 increases the distance “d” so that mold 14 and imprinting layer 24are spaced-apart.

[0026] Referring to FIG. 4, additional processing may be employed tocomplete the patterning of substrate 10. For example, substrate 10 andimprinting layer 24 may be etched to increase the aspect ratio ofrecesses 30 in imprinting layer 24. To facilitate etching, the materialfrom which imprinting layer 24 is formed may be varied to define arelative etch rate with respect to substrate 10, as desired. Therelative etch rate of imprinting layer 24 to substrate 10 may be in arange of about 1.5:1 to about 100:1. Alternatively, or in addition to,imprinting layer 24 may be provided with an etch differential withrespect to photo-resist material (not shown) selectively disposed onside 24 c. The photoresist material (not shown) may be provided tofurther pattern imprinting layer 24, using known techniques. Any etchprocess may be employed, dependent upon the etch rate desired and theunderlying constituents that form substrate 10 and imprinting layer 24.Exemplary etch processes may include plasma etching, reactive ionetching, chemical wet etching and the like.

[0027] Referring to FIG. 5, a problem addressed by the present inventionconcerns formation of features on substrates having extreme topologieswhen compared to the dimensions of features formed thereon. As a result,substrate 10 appears to present a non-planar surface 12. This has beentraditionally found in substrates formed from gallium arsenide (GAs) orindium phosphide (InP). However, as the feature dimensions decreasesubstrates that have historically been considered planar may present anon-planar surface to features formed thereon. For example, substrate 10is shown with variations in surface height. The variation in heightfrustrates attempts to control the dimensions of features formed intosubstrate 10, because of the resulting differences in distances betweennadirs 130 a and 160 a from surface 12, shown as h₁ and h₂,respectively. The height differential, Δh, between surface nadir 130 aand nadir 160 a is defined as follows:

Δh=|h ₁ −h ₂|  (1)

[0028] Height differential, Δh, results in differing etchcharacteristics of vias formed into substrate 10, discussed more fullybelow with respect to FIGS. 6 and 7.

[0029] Referring to FIGS. 5, 6 and 7, transfer of the features, such asrecesses 131, 141, 151, 161 and subportions 24 a, in imprinting layer 24into substrate 10 occurs through etch processes. The heightdifferential, Δh, results during formation of via 261 in substrate 10before formation of the remaining vias, which will be formed in regionsof substrate 10 in superimposition with recesses 131, 141 and 151. Thisresults from the time during which substrate 10 is etched duringformation of vias. Specifically, nadir 160 a reaches surface 12 ofsubstrate 10 before the remaining nadirs 130 a, 140 a and 150 a. As aresult an etch differential occurs, i.e., the etch process to whichsubstrate 10 is exposed to form vias therein differs over substratesurface 12. The etch differential is problematic, because it results inanisotropic etching that distorts the features transferred intosubstrate 10 from imprinting layer 24. The distortion presents, interalia, by variations in width w₃ between vias 231, 241, 251 and 261formed into substrate 10.

[0030] Ideally, the width of recesses 131, 141, 151 and 161, w₁, shouldbe substantially similar to width w₃. However the height differential,Δh, results in w₃ of vias 251 and 261 being greater than w₁, as well aslarger than w₃ of vias 231 and 241. The difference between the widths w₃of vias 231, 241, 251 and 261 defines a differential width Δw. Thegreater the height differential, Δh, the greater the differential widthΔw. As a result Δw of via 231 and 261 is greater than Δw of vias 231 and251.

[0031] Referring to both FIGS. 4, 6, 7 and 8, to avoid these drawbacks,the present invention seeks to minimize the height differential Δh byminimizing layer thickness t₂ and selecting a region of substrate 10upon which to locate and define area, A, so as to maximize the planarityof area A. Optimized production yield favors maximization of area A.However, it was determined that the smaller area, A, is made, thegreater the planarity of substrate surface 12 in area, A. In short,minimization of area, A, maximizes the planarity of the same. Thus,attempts to obtain large production yields, appears to be in conflictwith maximizing the planarity of area, A, because maximizing the area Areduces the planarity of surface 12 associated with area, A.

[0032] The manufacture of metrology standards, however, does not requirelarge yields. Therefore, in the present embodiment of the invention, thelocation and size of area, A, is chosen to maximize the planarity ofsurface 12 in area, A of surface 12 over which vias 231, 241, 251 and261 are formed. It is believed that by appropriately selecting area, A,over which vias 231, 241, 251 and 261 are formed, it will be possible todeposit an imprinting layer 24 of sufficiently small thickness t₂ whileminimizing height differential Δh, if not abrogating the heightdifferential Δh entirely. This provides greater control over thedimensions of recesses 131, 141, 151 and 161, that may be subsequentlyformed into imprinting layer 24, thereby affording the fabrication offeatures on the order of a few nanometers.

[0033] Referring to FIGS. 1, 4 and 8, to that end, the minimum layerthickness was chosen to avoid visco-elastic behavior of the liquid inbeads 25. It is believed that visco-elastic behavior makes difficultcontrolling the imprinting process. For example, the visco-elasticbehavior defines a minimum thickness that layer 24 may reach, afterwhich fluid properties, such as flow, cease. This may present by bulgesin nadirs 130 a, 140 a, 150 a and 160 a as well as other problematiccharacteristics. In the present embodiment it was determined thatproviding imprinting layer 24 with a minimum thickness t₂ of no lessthan approximately 10 nanometers satisfied this criteria, i.e., it wasthe minimum thickness that could be achieved while preventing imprintinglayer 24 from demonstrating visco-elastic behavior. Assuming a uniformthickness, t₂, over layer 24, e.g., sub-portions 24 a and recesses 131,141, 151 and 161 not being present so that side 24 c is planar it wasdetermined that the volume of liquid in beads 25 may define theplanarity of side 24 d that forms an interface with surface 12 and isdisposed opposite to side 24 c. The volume is typically selected tomaximize the planarity of side 24 d, which forms an interface withsurface 12. With a priori knowledge of the topology of surface 12, thesize and locus of area, A, may be chosen to maximize planarity over areaA. Knowing A and the desired layer thickness t₂, the volume, V, may bederived from the following relationship:

V=At₂  (2)

[0034] However, with the presence of features, such as sub-portions 24 aand recesses 131, 141, 151 and 161, results in layer 24 having a varyingthickness over area, A. Thus, equation (2) is modified to take intoconsideration volumetric changes required due to the varying thicknessof layer 24 over area, A. Specifically, the volume, V, is chosen so asto minimize thickness t₂, while avoiding visco-elastic behavior andproviding the requisite quantity of liquid to include features, such assub-portions 24 a of thickness t₁, and recess 131, 141, 151 and 161 intolayer 24. As a result, in accordance with this embodiment of theinvention, the volume, V, of liquid in beads 25 may be defined asfollows:

V=A(t ₂ +ft ₁)  (3)

[0035] where f is the fill factor and A, t₂ and t₁ are as defined above.

[0036] Referring to FIGS. 1, 4, 7, 8 and 9, further control of thedimensions of features formed into substrate 10 may be achieved byproper placement and selection of recessions 16 and protrusions 18 oversurface 14 a. Specifically, the arrangement of recessions 16 andprotrusions 18 on mold 14 may be designed to define a uniform fillfactor over mold surface 14 a. As a result, the size of etch areas willbe substantially equal to the size of non-etch areas of substrate 10 inarea A, where features on mold surface 14 a are imprinted. Thisarrangement of features reduces, if not avoids, variations in imprintinglayer 24 thickness by minimizing pattern density variations. By avoidingthickness variations in imprinting layer 24, distortions caused by thetransfer of features into substrate 10 during etch processes arereduced, if not avoided. Additional control can be obtained by havingthe recessions 16 and protrusions 18 formed to be periodic over surface14 a of mold 14. As a result, the features transferred to imprintinglayer 24 and subsequently etched into area A, i.e., vias 231, 241, 251and 261, fully populate and are periodic in area A.

[0037] It should be noted that mold surface 14 a may be formed withuniform period features having common shapes, as well as havingdiffering shapes, as shown. Further, recessions 16 and protrusions 18may be arranged on mold 14 to form virtually any desired geometricpattern. Exemplary patterns include a series of lineargrooves/projections 80, a series of L-Shaped grooves/projections 82, aseries of intersecting grooves/projections defining a matrix 84, and aseries of arcuate grooves/projections 86. Additionally, pillars 88 mayproject from mold 14 and have any cross-sectional shape desired, e.g.,circular, polygonal etc.

[0038] Additionally, it is desired not to employ features as part of themetrology standards that are located proximate to the edge of imprintinglayer 24 and, therefore, area A. These features become distorted whentransferred into substrate 10 during etching. The distortion is producedby edge-effects due to microloading, thereby exacerbating control of thefeature dimensions.

[0039] Referring to FIGS. 7 and 8, in another embodiment of the presentinvention, further control of formation of vias 231, 241, 251 and 261may be achieved by orientating the lattice structure of substrate 10 toensure that sidewalls 231 a, 241 a, 251 a and 261 a are orientated to besubstantially parallel to one of the crystal planes of the material fromwhich the substrate 10 is formed. For example, substrate 10 may befabricated so that the sidewalls 231 a, 241 a, 251 a and 261 a extendparallel to either of the 100, 010 or the 110 planes. This facilitatesmore precise control of the width w₃ of vias 231, 241, 251 and 261 infurtherance of uniformity of the same among all features formed in areaA, particularly when features of imprinting layer 24 are transferredinto substrate 10 using wet etch chemistries.

[0040] Referring to FIG. 1 in accordance with another embodiment of thepresent invention, to further provide greater control of the featuredimensions in imprinting layers 24, it has been found that the force{overscore (F)} applied by mold 14 should be deminimis and onlysufficient magnitude to facilitate contact with beads 25. The spreadingof liquid in beads 25 should be attributable primarily through capillaryaction with mold surface 14 a.

[0041] Referring to FIGS. 1, 2 and 4, the characteristics of material 25a are important to efficiently pattern substrate 10 in light of theunique deposition process that is in accordance with the presentinvention. As mentioned above, material 25 a is deposited on substrate10 as a plurality of discrete and spaced-apart beads 25. The combinedvolume of beads 25 is such that the material 25 a is distributedappropriately over area of surface 12 where imprinting layer 24 is to beformed. As a result, imprinting layer 24 is spread and patternedconcurrently, with the pattern being subsequently set by exposure toradiation, such as ultraviolet radiation. It is desired, therefore, thatmaterial 25 a has certain characteristics to facilitate even spreadingof material 25 a in beads 25 over surface 12 so that the all thicknessest₁ are substantially uniform and all thickness t₂ are substantiallyuniform and all widths, w₁, are substantially uniform. The desirablecharacteristics include having a suitable viscosity to demonstratesatisfaction with these characteristics, as well as the ability to wetsurface of substrate 10 and avoid subsequent pit or hole formation afterpolymerization. To that end, in one example, the wettability ofimprinting layer 24, as defined by the contact angle method, should besuch that the angle, θ₁, is defined as follows:

0>θ₁<75°  (4)

[0042] With these two characteristics being satisfied, imprinting layer24 may be made sufficiently thin while avoiding formation of pits orholes in the thinner regions of imprinting layer 24.

[0043] Referring to FIGS. 2, 3, 4 and 5, another desirablecharacteristic that it is desired for material 25 a to possess isthermal stability such that the variation in an angle Φ, measuredbetween a nadir 30 a of a recess 30 and a sidewall 30 b thereof, doesnot vary more than 10% after being heated to 75° C. for thirty (30)minutes. Additionally, material 25 a should transform to material 25 c,i.e., polymerize and cross-link, when subjected to a pulse of radiationcontaining less than 5 J cm−². In the present example, polymerizationand cross-linking was determined by analyzing the infrared absorption ofthe “C═C” bond contained in material 25 a. Additionally, it is desiredthat substrate surface 12 be relatively inert toward material 25 a, suchthat less than 500 nm of surface 12 be dissolved as a result sixty (60)seconds of contact with material 25 a. It is further desired that thewetting of mold 14 by imprinting layer 24 be minimized, i.e., wettingangle, θ₂, be should be of requisite magnitude. To that end, the wettingangle, θ₂, should be greater than 75°.

[0044] The constituent components that form material 25 a to provide theaforementioned characteristics may differ. This results from substrate10 being formed from a number of different materials. As a result, thechemical composition of surface 12 varies dependent upon the materialfrom which substrate 10 is formed. For example, substrate 10 may beformed from silicon, plastics, gallium arsenide, mercury telluride, andcomposites thereof. Additionally, substrate 10 may include one or morelayers in region, e.g., dielectric layer, metal layers, semiconductorlayer and the like.

[0045] Referring to FIGS. 2 and 3, in one embodiment of the presentinvention, the constituent components of material 25 a consist ofacrylated monomers or methacrylated monomers that are not silyated, across-linking agent, and an initiator. The non-silyated acryl ormethacryl monomers are selected to provide material 25 a with a minimalviscosity, e.g., viscosity approximating the viscosity of water (1-2cps) or less. However, it has been determined that the speed ofimprinting may be sacrificed in favor of higher accuracy in featuredimensions. As a result, a much higher viscosity material may beemployed. As a result the range of viscosity that may be employed isfrom 1 to 1,000 centipoise or greater. The cross-linking agent isincluded to cross-link the molecules of the non-silyated monomers,providing material 25 a with the properties to record a pattern thereonhaving very small feature sizes, on the order of a few nanometers and toprovide the aforementioned thermal stability for further processing. Tothat end, the initiator is provided to produce a free radical reactionin response to radiation, causing the non-silyated monomers and thecross-linking agent to polymerize and cross-link, forming a cross-linkedpolymer material 25 c. In the present example, a photo-initiatorresponsive to ultraviolet radiation is employed. In addition, ifdesired, a silyated monomer may also be included in material 25 a tocontrol the etch rate of the resulting cross-linked polymer material 25c, without substantially affecting the viscosity of material 25 a.

[0046] Examples of non-silyated monomers include, but are not limitedto, butyl acrylate, methyl acrylate, methyl methacrylate, or mixturesthereof. The non-silyated monomer may make up approximately 25% to 60%by weight of material 25 a. It is believed that the monomer providesadhesion to an underlying organic transfer layer, discussed more fullybelow.

[0047] The cross-linking agent is a monomer that includes two or morepolymerizable groups. In one embodiment, polyfunctional siloxanederivatives may be used as a cross-linking agent. An example of apolyfunctional siloxane derivative is1,3-bis(3-methacryloxypropyl)-tetramethyl disiloxane. Another suitablecross-linking agent consists of ethylene diol diacrylate. Thecross-linking agent may be present in material 25 a in amounts of up to20% by weight, but is more typically present in an amount of 5% to 15%by weight.

[0048] The initiator may be any component that initiates a free radicalreaction in response to radiation, produced by radiation source 22,shown in FIG. 1, impinging thereupon and being absorbed thereby.Suitable initiators may include, but are not limited to,photo-initiators such as 1-hydroxycyclohexyl phenyl ketone orphenylbis(2,4,6-trimethyl benzoyl) phosphine oxide. The initiator may bepresent in material 25 a in amounts of up to 5% by weight, but istypically present in an amount of 1% to 4% by weight.

[0049] Were it desired to include silylated monomers in material 25 a,suitable silylated monomers may include, but are not limited to,silyl-acryloxy and silyl methacryloxy derivatives. Specific examples aremethacryloxypropyl tris(tri-methylsiloxy)silane and(3-acryloxypropyl)tris(tri-methoxysiloxy)-silane. Silylated monomers maybe present in material 25 a in amounts from 25% to 50% by weight. Thecurable liquid may also include a dimethyl siloxane derivative. Examplesof dimethyl siloxane derivatives include, but are not limited to,(acryloxypropyl) methylsiloxane dimethylsiloxane copolymer.

[0050] Referring to both FIGS. 1 and 2, exemplary compositions formaterial 25 a are as follows:

COMPOSITION 1 n-butylacrylate+(3-acryloxypropyltristrimethylsiloxy)silane+1,3bis(3-methacryloxypropyl)tetramethyldisiloxaneCOMPOSITION 2 t-n-butylacrylate+(3-acryloxypropyltristrimethylsiloxy)silane+Ethylene dioldiacrylate COMPOSITION 3 t-butylacrylate+methacryloxypropylpentamethyldisiloxane+1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane

[0051] The above-identified compositions also include stabilizers thatare well known in the chemical art to increase the operational life, aswell as initiators. Further, to reduce distortions in the features ofimprinting layer 24 due to shrinkage of material 25 a during curing,e.g., exposure to actinic radiation such as ultraviolet radiation,silicon nano-balls may be added to the material 25 a either beforepatterning, e.g., before application of beads 25 to surface 12, or afterapplication of beads 25 to surface 12.

[0052] Referring to FIGS. 1, 2 and 3, additionally, to ensure thatimprinting layer 24 does not adhere to mold 14, surface 14 a may betreated with a modifying agent. One such modifying agent is a releaselayer (not shown) formed from a fluorocarbon silylating agent. Therelease layer and other surface modifying agents, may be applied usingany known process. For example, processing techniques that may includechemical vapor deposition method, physical vapor deposition, atomiclayer deposition or various other techniques, brazing and the like. Inthis configuration, imprinting layer 24 is located between substrate 10and release layer (not shown), during imprint lithography processes.

[0053] Referring to FIGS. 4 and 10, in some cases the non-planartopology of substrate 110 may frustrate deposition of an imprintinglayer 24. This may be overcome by the use of a planarization layer 125.Planarization layer 125 functions to present a planar surface 125 a toimprinting layer 124, shown more clearly in FIG. 11.

[0054] Referring to both FIGS. 10 and 11, planarization layer 125 may beformed from a number of differing materials, such as, for example,thermoset polymers, thermoplastic polymers, polyepoxies, polyamides,polyurethanes, polycarbonates, polyesters, and combinations thereof. Inthe present example, planarization layer 125 is formed from an aromaticmaterial so as to possess a continuous, smooth, relatively defect-freesurface that may exhibit excellent adhesion to the imprinting layer 124.Specifically, surface 125 a presents a planar region upon whichimprinting layer 124 may be disposed and recesses 331, 341, 351 and 361are formed.

[0055] Planarization layer 125 may be disposed on substrate 110 usingany known deposition technique. In the present example, planarizationlayer 125 is disposed on substrate 110 using spin-on techniques.However, it was discovered that during etching, that the difference inheight between nadirs 330 a and 360 a from surface 112, shown as h₃ andh₄, respectively, results in differing etch characteristics of viasformed into substrate 110, for the reasons discussed above. The heightdifferential between surface nadir 330 a and nadir 360 a is defined asfollows:

Δh′=|h ₃ −h ₄|  (5)

[0056] Referring to both FIGS. 11 and 12, during the etching process,the features in imprinting layer 124, such as sub-portions 224 a aretransferred into both planarization layer 125 and substrate 110, formingsub-portions 225 a. Spaced apart between sub-portions 225 a are vias431, 441, 451 and 461. Due to height differential Δh′ anisotropicetching occurs that distorts the features transferred into substrate 110from imprinting layer 124, as discussed above. To avoid the problemspresented by the height differential Δh′ the solutions described abovemay apply with equal weight here. An additional advantage with providingplanarization layer 125 is that it may be formulated to compensate forthe anisotropicity of the etch that occurs due to the heightdifferential, Δh, defined by equation 1. As a result, planarizationlayer may be employed to reduce, if not overcome, the deleteriouseffects of the height differential, Δh, defined by equation 1.

[0057] The embodiments of the present invention described above areexemplary. Many changes and modifications may be made to the disclosurerecited above, while remaining within the scope of the invention. Forexample, as mentioned above, many of the embodiments discussed above maybe implemented in existing imprint lithography processes that do notemploy formation of an imprinting layer by deposition of beads ofpolymerizable material. Exemplary processes in which differingembodiments of the present invention may be employed include a hotembossing process disclosed in U.S. Pat. No. 5,772,905, which isincorporated by reference in its entirety herein. Additionally, many ofthe embodiments of the present invention may be employed using a laserassisted direct imprinting (LADI) process of the type described by Chouet al. in Ultrafast and Direct Imprint of Nanostructures in Silicon,Nature, Col. 417, pp. 835-837, June 2002. Therefore, the scope of theinvention should be determined not with reference to the abovedescription, but instead should be determined with reference to theappended claims along with their full scope of equivalents.

What is claimed is:
 1. A method of forming a layer on a substrate tofacilitate fabrication of metrology standards, said method comprising:creating a flowable region on said substrate, defining a fluid state,with said flowable region having a volume associated therewith; anddefining a layer over an area of said region having opposed sides, oneof which faces said substrate, defining an interface, with said opposedside facing away from said substrate, said layer having a thicknessmeasured between said opposed sides, with said volume being selected tomaximize a planarity of said interface over said area.
 2. The method asrecited in claim 1 wherein said thickness is selected to minimizevisco-elastic properties of in said flowable region liquid in saidlayer.
 3. The method as recited in claim 2 wherein said thickness is noless than 10 nano-meters.
 4. The method as recited in claim 1 furtherincluding solidifying said region, defining a solidified state, withsaid flowable region consisting of material to minimize dimensionalchanges of said material when transitioning between said liquid andsolidified states.
 5. The method as recited in claim 1 wherein creatingfurther includes depositing, upon said substrate, a bead ofpolymerizable material and defining further includes contacting saidliquid bead with a mold having a relief structure on a surface thereofto create a recess in said side facing away from said substrate andsubjecting said layer to conditions to polymerize said polymerizablematerial, forming a polymerized layer.
 6. The method as recited in claim5 wherein contacting further includes contacting said liquid with saidmold having a plurality of relief structures formed from multiplerecessions and protrusions formed into said surface to create aplurality of said recess on said side facing away from said substrate,with said multiple recessions and protrusions arranged to provide saidsurface with a substantially uniform fill factor.
 7. The method asrecited in claim 5 wherein contacting further includes contacting saidliquid with said mold having a plurality of periodic relief structuresformed from multiple recessions and protrusions formed into saidsurface.
 8. The method as recited in claim 5 wherein contacting furtherincludes contacting said liquid with said mold with minimal force toachieve spreading primarily through capillary action of said liquid withsaid surface.
 9. The method as recited in claim 5 wherein said substratehas a crystalline structure and said recess has a nadir and furtherincluding etching said layer and said substrate to form a via in saidregion of said substrate in superimposition with said nadir, with saidvia having walls that extend transversely to said nadir and parallel toa 110 plane of said crystalline structure.
 10. A method of forming alayer on a substrate to facilitate fabrication of metrology standards,said method comprising: depositing a bead of liquid upon said substrate,with said bead having a volume associated therewith; and spreading saidbead over an area of said substrate to define a layer having first andsecond opposed sides, which is in a liquid state, with said first sidefacing said substrate and having a planarity associated therewith, withsaid second side facing away from said substrate, said layer having aminimum thickness measured between said first and second sides, withsaid planarity, for said minimum thickness, being defined by saidvolume, and said minimum thickness selected to reduce visco-elasticproperties of said liquid in said layer.
 11. The method as recited inclaim 10 including solidifying said layer, defining a solidified state,with said layer consisting of material to minimize dimensional changesof said material when transitioning between said liquid and solidifiedstates.
 12. The method as recited in claim 11 wherein said bead ofviscous liquid is a polymerizable material and spreading furtherincludes contacting said liquid bead with a mold having a plurality ofrelief structures defined by multiple recessions and protrusions, formedinto a surface of said mold, to create a plurality of recesses on saidsecond side, with said multiple recessions and protrusions arranged toprovide said surface with a substantially uniform fill factor, andsubjecting said layer to conditions to polymerize said polymerizablematerial, forming a polymerized layer.
 13. The method as recited inclaim 12 further including arranging said plurality of relief structureson said mold to be periodic.
 14. The method as recited in claim 13wherein contacting further includes contacting said liquid with saidmold with minimal force to achieve spreading primarily through capillaryaction of said liquid with said surface.
 15. The method as recited inclaim 14 wherein said substrate has a crystalline structure and saidrecess has a nadir and further including etching said layer and saidsubstrate to form a via in a region of said substrate in superimpositionwith said nadir, with said via having walls that extend transversely tosaid nadir and parallel to a 110 plane of said crystalline structure.16. A method for forming a layer on a substrate to facilitatefabrication of metrology standards, said method comprising: depositing abead of polymerizable viscous liquid upon said substrate, with said beadhaving a volume associated therewith; spreading said bead over an areaof said substrate by contacting said bead with a mold having a pluralityof relief structures defined by multiple recessions and protrusions,formed into a surface of said mold, to define a layer having first andsecond opposed sides, with said first side facing said substrate andhaving a planarity associated therewith and said second side facing awayfrom said substrate and having a plurality of recesses therein, each ofwhich has a nadir, said layer having a thickness measured between saidfirst side and a plane coplanar with each of the nadirs associated withsaid plurality of recesses, with said planarity being defined by saidvolume; and subjecting said layer to conditions to polymerize saidpolymerizable material, forming a polymerized layer.
 17. The method asrecited in claim 16 wherein said thickness is selected to minimizevisco-elastic properties of said liquid in said layer.
 18. The method asrecited in claim 16 wherein said multiple recessions and protrusions arearranged to provide said surface with a substantially uniform fillfactor and further including placing silicon nano-balls into saidviscous liquid.
 19. The method as recited in claim 16 wherein contactingfurther includes contacting said bead with said mold with a requisiteforce to achieve spreading primarily through capillary action of saidliquid with said surface.
 20. The method as recited in claim 16 whereinsaid substrate has a crystalline structure and further including etchingsaid layer and said substrate to form a via in regions of said substratein superimposition with the nadir of each of said plurality of recesses,with said via having walls that extend transversely to said nadir andparallel to a 110 plane of said crystalline structure.